JPS63159868A - Developing method - Google Patents

Abstract

PURPOSE:To obtain an image having picture quality by allowing two maximum values of the intensity of a magnetic field in the tangential direction on the surface of a developer carrying body to exist by inserting and holding a developer and the most adjacent part of a latent image carrying body between them, and setting the magnitude of the minimum value of a magnetic field in the tangential direction of the most adjacent part, to a prescribed ratio or above of the magnitude of the maximum value. CONSTITUTION:A photosensitive drum 1, and a conductive sleeve being a developer carrying body having a magnetic field generating device on the back are provided. Also, on the surface of the sleeve 2, a developer layer in which a magnetic grain and a non-magnetic grain have been mixed is provided, a horizontal magnetic field of the magnetic field generating device of the back of the sleeve 2 is operated, and a bias voltage by a series power source of a DC 5 and an AC 6 is applied to a development interval. In this state, by forming a magnetic field distribution in the tangential direction so that two maximum values of the intensity of a magnetic field in the tangential direction on the surface of the sleeve 2 exist by inserting and holding sleeve 2 and the most adjacent part of the drum 1 between them, and magnitude of the maximum value of the intensity of a magnetic field in the tangential direction in the vicinity of the most adjacent part becomes >=90% of the maximum value, a uniform developer layer is formed at a developing position.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a developing method for developing a latent image, which is also applicable to Victorian color.

[Conventional technology]

Conventionally, as one of the developing methods, an insulating magnetic toner or a non-magnetic toner is applied thinly to the surface of a developer carrier, and a layer is formed between the surface of this thin layer of developer and the surface of the latent image carrier in a developing section. JP-A-55-18656 discloses a method in which an electrostatic latent image on a latent image carrier is developed by forming a gap in the developing area and applying an alternating electric field to the developing section to cause the toner to fly from above the developer carrier. has been disclosed.

However, such a developing method has the following problems. In other words, if you try to reliably charge each toner particle on the developer carrier surface to the desired polarity, the thickness of the toner layer on the developer carrier surface will inevitably become thinner, and the developed density of the solid black area will not be sufficient. The problem is that high values cannot be obtained.

Furthermore, Japanese Patent Application Laid-open No. 55-32060 and Japanese Patent Application Laid-open No. 153970, in which a two-component developer is used and developed by applying an alternating electric field in a developing section, improve image quality and image density. It is known to have excellent effects.

However, even with this excellent developing method, when high-speed development is performed, if the state of the developer supplied to the developing section changes to some extent,
Insufficient toner density in solid black areas was observed.

This lack of toner concentration in solid black areas is more pronounced when developing with non-magnetic toner made mainly of resin than when developing with magnetic toner made of resin and magnetic material. is more prominent. Therefore, it has been found that this problem is more problematic when performing color development than black and white development.

In particular, for high-quality image development aiming at Victorian colors, edge effects and lack of density in solid black areas become serious problems.

Therefore, when the thickness of a layer of toner on the surface of the developer carrier is increased, it becomes difficult for each toner to be charged to the desired polarity and charge amount, especially in one-component development. For this reason, not only did excess toner adhere to non-image areas, but also the resulting toner image was poor in quality.

Furthermore, in view of this background, the present applicant filed Japanese Patent Application No. 1887-1987 for an even more superior developing system. The content is a developer in which magnetic particles containing 40 wt% or more of magnetic powder and non-magnetic particles mainly made of resin are mixed on the surface of a latent image carrier and a developer carrier having a magnetic field generating means on the back surface. In the developing section, the magnetic poles of the magnetic field generating means on the back surface of the developer carrier are made to face the latent image carrier, and the strength of the magnetic field in the tangential direction on the surface of the developer carrier is set to 20.
0 Gauss or more, and maintains a development gap larger than the thickness of the developer layer, and forms an alternating electric field in the development gap to restrain the magnetic particles on the surface of the developer carrier. image area from the developer layer on the carrier to the latent image carrier;
This is a developing method in which development is performed by alternately repeating the process of making non-magnetic particles fly in both non-image areas and the process of returning excess non-magnetic particles to the developer carrier. According to this, it is possible to obtain a high-quality developed image that has little edge effect, sufficient solid black density, and is applicable to uniform Victorian color development. Further, even when an alternating electric field is applied to the developing section, the magnetic particles serving as the carrier do not transfer to the latent image carrier, and there is an advantage that stable and clear color image quality can always be obtained.

However, even with this excellent development method, when trying to achieve high-quality and high-speed images by reducing the particle size of the developer, the image density was insufficient (to solve this problem, the strength of the alternating electric field was increased). However, magnetic carrier particles began to adhere to the surface of the electrostatic image carrier, causing a large change in the concentration of the developer in the developer container, resulting in the inconvenience that the density of the developed image could not be controlled.

Even when the speed is increased, it is necessary to increase the rotational speed of the sleeve, which is a developer carrier, in order to increase the density.

In this case as well, centrifugal force acts on the carrier as the rotational speed increases, making it easier for the carrier to adhere to the drum, resulting in the same problem as above.

As described above, it has been extremely difficult to obtain high-speed, high-resolution images over a long period of time using conventional methods.

[Purpose of the invention]

The present invention eliminates the drawbacks of the above-mentioned conventional examples, and makes it possible to obtain high-quality, high-definition images over a long period of time that have little edge effect and have sufficient solid black density and can be applied to Victorian colors. Moreover, it is an object of the present invention to provide a developing method that can sufficiently handle high-speed processing.

[Summary of the invention]

The present invention achieves the above object, and includes a latent image holder;
A developer layer in which magnetic particles and developer particles are mixed is supported on the surface of a developer carrier having a magnetic field generating means on the back surface, and a magnetic field is generated on the back surface of the developer carrier in the development section with the latent image carrier. A horizontal magnetic field of the means is applied and a development gap larger than the thickness of the developer layer is maintained, and an alternating electric field is formed in the development gap to develop the latent image while restraining the magnetic particles on the surface of the developer carrier. In the developing method, there are two maximum values of the strength of the magnetic field in the tangential direction on the surface of the developer carrier, sandwiching the closest part between the developer carrier and the latent image carrier, and in the vicinity of the closest part. This developing method is characterized by forming a tangential magnetic field strength distribution in which the minimum value of the tangential magnetic field strength is 90% or more of the maximum value.

Further, in a preferred embodiment of the present invention, the horizontal magnetic field is formed using particles with an average particle size of 7 μm or less as the developer particles and particles with an average particle size of 30 μm or more and 90 μm or less as the magnetic particles. The maximum value of the magnetic field strength in the perpendicular direction on the surface of the developer carrier at the magnetic pole position of the magnetic field generating means is set to 800 Gauss or more, respectively, and the magnetic field in the tangential direction on the surface of the developer carrier in the vicinity of the nearest portion is The maximum value of the strength is to be 700 Gauss or more.

According to the present invention, it is possible to prevent magnetic particles from adhering to an electrostatic image carrier due to high-speed rotation of a developer carrier during high-speed development, and to strengthen the electric field strength of the alternating electric field, thereby supporting electrostatic image-bearing of magnetic particles. It can also prevent adhesion to the body, and high-quality developed images without fog can be achieved with high-speed development.

According to the present inventors, if the particle size of the toner particles is set to 7 μm or less on a volume average even if the particle size is small, the toner particles forming an image can be arranged in a convenient manner (corresponding appropriately to the latent image potential and fogging can be prevented). In particular, it has been found that if the average value is set in the range of 4 μm or more and 6 μm or less, a two-component image under an alternating electric field can be obtained without fogging, and in addition, an image close to printing can be obtained.

However, in this case, in order to increase the density, it is necessary to increase the peak value of the alternating electric field to about 1.5 to 2 times that when developing a normal 10 μm toner, and a good image quality can be obtained. . However, because the developing bias is high, magnetic particles tend to adhere to the drum, and if development is carried out over a long period of time, the magnetic particles attached to the drum will damage the drum surface, causing white spots on the image. or
Moreover, the amount of carrier in the developing machine changes. In other words, even though this toner is used, its effects cannot be obtained, and the density control of the developer does not work well, resulting in problems such as fogging. Embodiments of the present invention also solve these mutual problems.

〔Example〕

Hereinafter, the present invention will be explained in detail using Examples.

FIG. 3 is a schematic diagram of a developing device to which the developing method of the present invention is applied. In the figure, 1 is an electrostatic latent image holding member, 11 is a back electrode, and 12 is an electrostatic latent image holding layer thereon, which may be an insulating layer or an electrophotographic photoreceptor layer. Here, it is shown as a photosensitive drum 1. A developer carrier 2 is a conductive sleeve made of a non-magnetic material and rotates in the direction indicated by the arrow. Reference numeral 3 denotes a magnetic field generating means fixedly provided inside the sleeve, which in this example is a magnet roller having four magnetic poles. 4 is a developer in which magnetic particles containing magnetic powder in a resin are mixed with non-magnetic particles (toner) having a smaller average particle diameter and mainly made of resin. A developing bias is applied between the back electrode 11 of the photosensitive drum l rotating in the direction of arrow B and the sleeve 2 by a DC power source 5 and an AC power source 6.

7 is an elastic member, 8 is a toner supply roller, and 9 is a developer layer thickness regulating member, which is a doctor blade here.

A sleeve 2 is placed with a gap of 100 to 800 μm, preferably 200 to 500 μm, facing a photosensitive drum 1 having an electrostatic latent image on its surface and rotating in the direction of arrow B.

The toner replenishing roller 8, which has a plurality of recesses on its surface, rotates slowly as the drive gear of the sleeve 2 meshes with the drive gear of the photosensitive drum 1, and collects non-magnetic particles (toner) in the hopper part 9. T is dropped little by little into the lower developing chamber by the elastic member 7, and toner 'r is supplied.

The toner T supplied to the developing chamber is mixed with magnetic particles M (particles containing magnetic powder in resin) present near the surface of a sleeve 2 having a magnet roller 3 inside.

As the sleeve 2 rotates in the direction of the arrow, the developer 4 on the sleeve surface moves in the direction of arrow C, and the toner supplied by this movement gradually enters the inside of the developer 4 and is mixed. .

The mixed developer 4 is transferred by a doctor blade 10 formed of a non-magnetic material and fixed at a distance of about 100 to 550 μm, preferably 150 to 450 μm, from the surface of the sleeve 2, facing between the magnetic poles N1 and S. Appropriate thickness, for example 100 to 600 μm, preferably 150 to 5
00 μm and is applied to the surface of the sleeve 2.

This developer layer thickness is smaller than the drum-sleeve gap in the development area, so the developer layer and the drum surface are stationary and non-contact. The non-magnetic particles (toner) T in the applied developer 4 are triboelectrically charged due to friction with the magnetic particles M and friction with the sleeve 2, and in this state, static electricity is generated between the sleeve 2 rotating in the direction of the arrow. Due to the adhesion caused by force and the adhesion caused by electrostatic force between the magnetic particles and the magnetic particles, the magnetic particles are transported to the development area while remaining attached to the sleeve 2 as the sleeve 2 rotates.

It is thought that the development area is distributed on the upstream and downstream sides of the developer conveyance centering on the closest portion between the sleeve and the drum.

In the developing area, magnetic poles N and S of the magnet roller 3 inside the sleeve 2 are arranged to face each other with respect to the photosensitive drum l. Therefore, the developer on the surface of the sleeve 2 does not form spikes in the development area and has a uniform layer thickness. Therefore, it is not necessary to separate the photosensitive drum surface 12 and the sleeve 2 by, for example, about 1 mm or more while keeping the developer layer and the drum surface out of contact.

What is important here is that the doctor blade and the development position are set between the magnetic pole pairs of the same and different polarities so that the developer regulated by the doctor blade 10 does not pass through the magnetic pole position before reaching the development position. That's true. This means a region where the magnetic field has many horizontal components.

If the developer that has passed through the doctor blade passes through the magnetic pole position, the developer will stand up once at this magnetic pole position and become a loosened developer layer, making it difficult to reduce the layer thickness at the development position. . In order to solve this problem, trying to maintain a non-contact condition in the developing section by widening the space between the photosensitive drum and the sleeve will actually reduce the binding force of the developer in the developing section, resulting in carrier adhesion and poor development.

In addition, once the toner stands up, it causes uneven blistering in the developer layer, which occurs as unevenness in the image, especially in the solid black areas, which significantly deteriorates the impression of the image.

More preferably, in order to make the layer uniform, the regulation position of the doctor blade IO is preferably provided at an angle θ (FIG. 3) of 5° or more closer to the development position from the center of the upstream magnetic pole position.

In order to satisfy the above conditions, the magnetic pole distance between the N-polarity magnetic pole N and the S-polarity magnetic pole S1 must be at least 45° or more.
The preferred condition is that the opening is preferably 60° or more.

Further, as a feature of the method of the present invention, it is effective to use a toner having an average particle diameter of 7 μm or less, which is smaller in particle size than the toner normally used for high-quality image development. In this case, in order to sufficiently increase the density, it was necessary to increase the bias of the AC power source during development by 1.5 to 2 times the normal bias.

In this case, in order to perform good development, taking into account the centrifugal force of high-speed development, the horizontal magnetic field component on the sleeve surface at the development position was required to be 700 Gauss or more. In order to achieve this, the strength of the magnetic field in the vertical direction on the sleeve surface at N, S, was determined by experiment to be approximately 800 Gauss or more. If this horizontal magnetic force is weaker than this, the carrier will stick to the drum, disturbing the image, the balance between the carrier and toner inside the developing machine will be disturbed, causing fogging, and the drum or carrier may be damaged. Problems such as lack of durability arose. Therefore, it will be understood that the above conditions are important for achieving the purpose of the present invention.

By the way, magnetizing an isotropic magnet to satisfy these conditions is extremely expensive (though not impossible).In addition, in a developing device that is desired to be miniaturized, it is difficult to magnetize an isotropic magnet to satisfy these conditions. It has been found that there are cases in which a certain magnetic pole configuration cannot be obtained.In this case, it is possible to embed an anisotropic magnet in an isotropic magnet to generate the desired magnetic force, but in this case, the perpendicular magnetic field Because the strength is concentrated at the position of the magnetic pole, the developer is not conveyed well around the development position, and the uniform toner layer at the development position may sometimes change slightly. When the inventors studied this point in more detail, they were able to elucidate even more preferable conditions.

Figure 2 is a distribution diagram of the magnetic field on the magnet roll used in the present invention, and shows the perpendicular magnetic field component (magnetic pole strength), which is generally used to represent the strength of the magnetic field on the sleeve surface. It is. In the figure, the horizontal axis connecting the centers of the drum and sleeve is taken as the horizontal axis, and the part facing the drum is designated as 00. This vertical component indicates a magnetic field component in a direction perpendicular to the surface of the sleeve 2, and FIG. 2 shows this distribution over the circumference of the sleeve.

From this figure, the perpendicular magnetic field component between the magnetic poles N1 and Sl is O
You can see that it is Gaussian.

From this figure alone, only the distribution of the magnetic field in the vertical direction on the sleeve surface can be seen. Therefore, FIG. 1 shows a magnetic field distribution diagram showing horizontal magnetic field components on the surface of the sleeve, which is the developer carrier 2, with the angular coordinate axes in FIG. 2 fixed.

In the embodiment shown in FIG. 1, there are two maximum values of the magnetic force in the tangential direction between the magnetic poles N, S, with the sleeve closest to the drum in between.

In this case, there are local minimum values between the local maximum values. Normally, in such a case, the developer on the sleeve tends to be strongly attracted to a portion near the maximum value of the horizontal magnetic force in the tangential direction. For example, this phenomenon is remarkable in the case of magnetic field distributions as shown in FIGS. 4 and 5. FIG. 4 is a distribution diagram of the vertical magnetic field component, and FIG. 5 is a distribution diagram of the horizontal magnetic field component of the magnet.

When using a magnet with a magnetic field distribution like that shown in Figures 4 and 5, when the sleeve is rotated to convey the developer, the developer will reach the maximum horizontal magnetic force on the upstream side of the developer conveyance at the development position. Then, the developer jumps to the maximum value on the downstream side of the developer transport, and as a result, a uniform developer layer cannot be obtained at the development position. As a result of numerous experiments, in order to obtain a uniform increase in the developer layer at the development position, the fourth
As shown in the figure, it has been found that it is necessary to set the difference between the two maximum values and the minimum value near the development position to within 10% of the magnitude of the absolute value of the maximum value. Furthermore, as shown in FIG. 4 of this embodiment, if the maximum value of the horizontal magnetic field exists between the center of the development position (the part closest to the drum and sleeve), when the conveyance is stable, the maximum value of the horizontal magnetic field A more uniform solid density was obtained than with a magnet with a single value.

This can be explained as follows. FIGS. 6 and 7 show distribution diagrams of magnetic field components of conventional magnets. . FIG. 6 shows the distribution of the vertical magnetic field component, and FIG. 7 shows the distribution of the horizontal magnetic field component. In the case of the magnetic field distribution as shown in FIGS. 7 and 8, the conveyance of the developer is stable, and furthermore, since the binding force on the carrier is strong, a high-quality image without carrier adhesion can be obtained. However, since the restraining force on the carrier at the development position is strong, uniformity was somewhat insufficient when trying to obtain a solid image. However, when a magnet having the magnetic field distribution shown in FIG. 1, which is a feature of the present invention, is used, the conveying performance is stable at the development position, but the binding force of the carrier is weakened.

Therefore, when a developing bias is applied, not only the surface of the carrier but also the toner near the sleeve surface inside the carrier is developed. Therefore, a uniform solid density can be obtained. Since the carriers are restrained by the restraining force of the maximum value of the horizontal magnetic field downstream of the development position, the carriers do not adhere.

As explained above, there are two maximum values of the horizontal magnetic field component sandwiching the development position (the position closest to the drum of the sleeve), and the minimum value near the development position is set to be 90% or more of the maximum value. It has been found that by using this method, the conveyance of the developer can be stabilized, and a uniform image with sufficient solid density can be obtained.

Next, during development, alternating voltages are applied between the sleeve 2 and the back electrode 11 of the photosensitive drum 1 to form an alternating electric field in the developing area. At this time, the DC voltage from the DC power supply 5 and the AC voltage from the AC power supply 6 are superimposed to perform development. Also, it is optimal to use a bias voltage. Alternatively, only an alternating current voltage may be used as a bias. The alternating current voltage does not necessarily have to be a sine wave, but may be a rectangular wave.

The peak-to-peak value of the AC used is Vp-p=200~-
I K V , the frequency is f = 100 ~ 5 K Hz
Good.

[Example I] 1F#J image potential image potential 600v1 background potential V is OV
When , the peak-to-peak value too is the developing bias voltage.
ovpp, +15 to AC voltage with frequency 1.6 KHz
Development was carried out by superimposing a DC voltage of 0V. The non-magnetic particles used are toner particles containing thermoplastic resin (polystyrene) as a main component and having a particle size distribution shown in FIG. 8(b), and are particles that are negatively charged with respect to magnetic particles. Reversal development can also be performed by using positive polarity toner and selecting an appropriate DC voltage. The magnetic particles contain magnetite (F
Particles having a number average particle diameter of 50 μm were used by kneading and pulverizing 75% by weight of magnetic powder of e304). Better image quality can be obtained by mixing in this two-component mixed developer silica particles located between the two particles in terms of charging series in an amount of 1 weight % or less.

When the above development bias voltage is applied and the potential of the sleeve exceeds the threshold value in the negative voltage phase, the number of negatively charged non-magnetic particles (at the closest part between the drum L and the sleeve 2) Even in areas, non-image areas (image background)
However, it flies from the developer layer on the sleeve 2 to the photosensitive drum l.

However, in a phase of opposite polarity to the above, at least the excess non-magnetic particles undergo a reverse transition and return to the sleeve.

After repeating this process several times, the gap between the drum and the sleeve widens, the alternating electric field weakens, the flying particles disappear, and development ends. In order to weaken the alternating electric field, the applied voltage may be weakened.

What is important here is to prevent the magnetic particles from flying and transferring from the developer layer on the sleeve 2 to the photosensitive drum 1 after development. This is because when the magnetic particles transfer, the magnetic particles in the developing device gradually disappear, causing a significant shift in the ratio between the number of magnetic particles and the number of non-magnetic particles in the developer. If the toner/magnetic particles are significantly distorted, it will cause background fog.Therefore, it is important to restrain the magnetic particles on the sleeve surface by magnetic force.

What is more important is that the distance between the photosensitive drum 1 and the sleeve 2 is not too large, resulting in blurred image quality. If the magnetic poles face the drum in the developing area, the brushes will stand up, making it difficult to reduce the distance between the drum and the sleeve.

For this reason, the distance between the drum and sleeve should be set at 100 to 800.
It is important that the magnetic poles (between N and S) of the magnet roller 3 face the drum in the developing area so that μm1 can be preferably set to 200 to 500 μm.

In this example, the thickness of the developer layer in one developing area of 300 μm is set between the sleeve and the drum, and the magnetic force distribution in the vertical and horizontal directions on the surface of the developing sleeve is as shown in FIGS. 2 and 1. When development was carried out using the bias described above, a good quality image without fogging was stably obtained.

Further, as a toner, magnetic powder containing magnetic particles in a resin and having the same average particle diameter as in the above example was used, and good quality images were also obtained in this case.

The particle size of the magnetic carrier particles described above is preferably 30 μm or more on average and 90 μm or less on average. Further, the magnetic powder content of the magnetic particles is preferably 50% by weight or more. Although it is possible to use magnetic particles in which the entire magnetic particles are made of a magnetic material, it is preferable that the magnetic particles contain an insulating material such as a resin so as to exhibit insulation properties.

Further, particles having a magnetic core as a core and a resin coating around the core can easily be formed into spherical particles, and can be uniformly charged with tripostatic charges. In addition, charge control agents such as pigments and dyes are mixed into the resin that makes up the magnetic particles to create non-magnetic particles (toner).
By making it possible to charge the toner to the desired polarity and charge amount, better high-quality image development becomes possible.

Furthermore, the mixing ratio of toner and magnetic particles is 15 wt% to 45 w.
It was possible to obtain images with high developed density and no blur over a very wide range of t%. Therefore, there is an advantage that the toner concentration can be easily controlled. When the mixing ratio is less than 15 wt %, the developed density becomes thinner, and when it is more than 45 wt %, soil blurring occurs, and there have been cases in which a desirable density cannot be obtained.

In the explanation of FIG. 3, the sleeve 2 was rotated in the direction indicated by the arrow, but good image quality was obtained even when the sleeve 2 was rotated in the opposite direction to the arrow.

[Example 2] The distance between the photosensitive drum 1 and the sleeve 2 was set to 300 μm, and the thickness of the developer layer was regulated with a doctor blade to be 200 μm at the position closest to the photosensitive drum. The developer used was a mixture of non-magnetic particles and magnetic particles having the particle size distribution shown in FIG. 8(a), and the concentration ratio of the non-magnetic particles was 15 wt%.

In addition, the content of magnetic powder in the magnetic particles is 70 wt%,
Particles with an average particle size of 50 μm were used. Furthermore, the same arrangement of magnetic poles as in Example 1 was used.

Under such conditions, the latent image potential VD of the image area has negative polarity.
00V, when the background potential vL is Ov, positively charged particles are used as the non-magnetic particles (toner), and the developing bias voltage is V p -p = 1800 V, f = 4.
, 0 KHz (7) DC voltage -150V to AC voltage
When I superimposed it and did not develop it, only the specific magnetic particles flew and transferred to the image area (≠ potato;), and neither non-magnetic particles nor magnetic particles adhered to the non-image area, and there was no soil blurring. A good image was obtained.

In this case, since the particle size of the toner became smaller, the appropriate value of the mixing ratio of toner and magnetic particles also changed to a range of 10 wt% to 25 wt%. The appropriate value of the mixing ratio of toner and magnetic particles is determined in each case by the ratio of the particle sizes of toner and magnetic particles.

Since a developer with a small particle size is used, images with fine detail and high resolution can be obtained that are close to printed images. Although the bias voltage was high, the magnetic force was strong, so the carrier did not stick to the drum and high-definition images could be stably obtained over a long period of time.

Although the above explanation was about non-contact development, good images were obtained even with contact development. However, in this case, the range of the C ratio between the toner and the magnetic particles to obtain a good quality image is narrower than in the non-contact method, so it is very difficult to obtain a stable image, although it is not impossible.

There are two maximum values of the magnetic field strength in the tangential direction, sandwiching the closest part between the developer carrier and the latent image carrier, and a minimum value of the magnetic field strength in the tangential direction near the closest part. By forming the magnetic field strength distribution in the tangential direction so that the size is 909 stones or more, which is the maximum value, a uniform developer layer can be formed at the development position, and there is no edge and the density is even. A uniform, high-quality image was also obtained.

More preferably, the maximum value of the strength of the vertical magnetic field on the surface of the developer carrier at the magnetic pole position of the magnetic field generating means that forms the horizontal magnetic field is set at 800 Gauss or more, respectively, so that the developer near the nearest portion By setting the strength of the magnetic field in the tangential direction on the surface of the carrier to 700 Gauss or more, stable, high-quality images can be obtained at high speed over a long period of time even if the toner particles have a small particle size.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the tangential magnetic field distribution of the embodiment of the present invention, Fig. 2 is an explanatory diagram showing the perpendicular magnetic field distribution of Fig. 1, and Fig. 3 is an explanatory diagram showing the magnetic field distribution of Figs. 1 and 2. 4 to 7 are explanatory diagrams for explaining the circumstances leading to the present invention, and FIGS. 4 and 6 show the vertical direction of the magnetic roller. Magnetic field distribution diagram, Figure 5,
Figure 7 is a magnetic field distribution diagram in the horizontal direction of the magnet roller, and Figures 8 (a) and 8 (b) are volume distribution diagrams of the toner particle diameters used (7 μm or less and larger than 7 μm, respectively).
It is. In the figure, 1 is a photosensitive drum, 2 is a sleeve, 3 is a magnet roller, 4 is a developer, 5 and 6 are development bias power supplies, and 10 is a doctor blade. Toben 3rd place sparrow Tosa (white,%

Claims (3)

[Claims] (1) A developer layer containing a mixture of magnetic particles and developer particles is carried on the surface of a developer carrier having a latent image carrier and a magnetic field generating means on the back surface, and in a developing section with the latent image carrier. A developing method in which a horizontal magnetic field from a magnetic field generating means on the back side of the developer carrier is applied to form an alternating electric field in the development gap to develop a latent image while restraining magnetic particles on the surface of the developer carrier,
There are two maximum values of the strength of the magnetic field in the tangential direction on the surface of the developer carrier, sandwiching the closest part between the developer carrier and the latent image carrier, and the magnetic field in the tangential direction near the nearest part. A developing method characterized by forming a tangential magnetic field strength distribution in which the minimum value of the intensity is 90% or more of the maximum value. (2) The developing method according to claim 1, wherein the development gap is larger than the thickness of the developer layer. (3) Particles with an average particle size of 7 μm or less are used as the developer particles, and particles with an average particle size of 30 μm or more are used as the magnetic particles.
The maximum value of the strength of the vertical magnetic field on the surface of the developer carrier at the magnetic pole position of the magnetic field generating means for forming the horizontal magnetic field is set to 800 Gauss or more using particles of .mu.m or less, respectively, to the nearest neighbor. The developing method according to claim 1, wherein the maximum value of the strength of the magnetic field in the tangential direction on the surface of the developer carrier is 700 Gauss or more.